Advice wanted on canola oil.

Mark, a little quick Googling seems to indicate that it's lineolic acid that is the culprit behind canola oil's fishy odor problems, at least most of the work in bioengineering appears to have been directed at minimizing it.

That's linolenic acid, the 18-carbon monounsaturated omega-3 fatty acid. Apparently some of its auto-oxidation products result in a fishy smell. Heating (as during cooking) of course accelerates auto-oxidation.

I use peanut oil for my oriental cooking, olive oil for my European cooking.

-Paul W.

That's linolenic acid, the 18-carbon monounsaturated omega-3 fatty acid. Apparently some of its auto-oxidation products result in a fishy smell. Heating (as during cooking) of course accelerates auto-oxidation.

I use peanut oil for my oriental cooking, olive oil for my European cooking.

Thanks for the correction, Paul; this is finally starting to make sense. This thread has been educational. Before now, I had no clue that there were such things as both linoleic and linolenic acids (I take it chemists have a reason to use two such similar names?). I blame it all on Mark Lipton , whose spelling I picked up when he wrote:

Canola oil is 63% oleic and 20% lineolic acids, both of which are components of olive oil

Of course, what Mark meant was "linoleic" but when I started Googling, I didn't realize there were two different acids. From what I've read online, Mark was correct but what he didn't mention is that linolenic acid comprises about 10% of canola oil but is next to absent (~1%) in olive oil. So that linolenic is what causes the fishy smells makes sense, as do the efforts I've read about to drive canola and soybean oil linolenic acid to <2% and make them work for frying.

I still think people must vary in their sensitivity to these odors. Otherwise, I can't understand how anybody could fry with canola and not notice.

That's linolenic acid, the 18-carbon monounsaturated omega-3 fatty acid. Apparently some of its auto-oxidation products result in a fishy smell. Heating (as during cooking) of course accelerates auto-oxidation.

Thanks for the correction, Paul; this is finally starting to make sense. This thread has been educational. Before now, I had no clue that there were such things as both linoleic and linolenic acids (I take it chemists have a reason to use two such similar names?). I blame it all on Mark Lipton , whose spelling I picked up when he wrote:

Canola oil is 63% oleic and 20% lineolic acids, both of which are components of olive oil

Mea culpa, Mark. Yes, I did mean linoleic acid there, but my fingers got ahead of my brain I'm afraid. Interesting about linolenic acid, too. I wonder if the autoxidation products of linolenic acid match some of those of the fatty acids common to fish oil? As to the nomenclature, it's a common problem in my field. Students have a devil of a time keeping straight propionic acid from propiolic acid or pyrroline from pyrrolidine. Most of these names are historically derived with little regard for logic or convenience. In the case of oleic, linoleic and linolenic acids: they all have the same number of carbons and differ only in the number of unsaturations (oleic is monounsaturated, the other 2 polyunsaturated) and consequently are considered closely related. In fact, there are unsaturase enzymes found in plants that convert oleic -> linoleic -> linolenic. Because animals lack those enzymes and we need lineolenic acid to function properly, it's classified as an Essential Fatty Acid (EFA).

Mark Lipton

Biochemical common names are mostly historical and because of that distressingly complex and confusing. If you want to be completely precise, you can of course use the official IUPAC name, which is totally unambiguous, but except for simple compounds, good luck deciphering the IUPAC name without the rule book in front of you.

This discussion has caused me to drag out my Biochemistry textbook. The fatty acids we've been discussing are all in the octadecanoic (18-carbon) family. The family members are:

Stearic acid (saturated octadecanoic acid):
H3C-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

Oleic acid (monounsaturated 9-octadecenoic acid):
H3C-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

Linoleic acid (diunsaturated 9,12-Octadecadienoic acid):
H3C-CH2-CH2-CH2-CH2-CH=CH-CH2-CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

Alpha-linolenic acid (triunsaturated 9,12,15-Octadecatrienoic acid):
H3C-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

Gamma-linolenic acid (triunsaturated 6,9,12-Octadecatrienoic acid):
H3C-CH2-CH2-CH2-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-CH2-CH2-CH2-COOH

Linoleic (9,12-Octadecadienoic acid) and Gamma-Linolenic acid (6,9,12-Octadecatrienoic acid) are both in the category called omega-6 fatty acids because the first unsaturated (double) bond occurs six carbons away from the end of the chain opposite the carboxyl (-COOH) end. Both of these are precursors to the prostaglandins and leukotrienes, cellular signal compounds involved in the triggering of immune system responses to injury such as blood clotting, inflammation, and fever. Aspirin (acetosalicylic acid) and related substances work because they inhibit the synthesis of these compounds. But complete absence of these polyunsaturated fatty acids in the diet causes slow wasting away and eventual death. For this reason they are called essential fatty acids. Fortunately they're present in adequate amounts in any balanced diet.

Alpha-linolenic acid (9,12,15-Octadecatrienoic acid) is an example of an omega-3 fatty acid because the first unsaturated bond occurs three carbons away from the end of the chain. Omega-3 fatty acids are synthesized into a series of prostaglandins and leukotrienes that (in humans) are less powerful in their effects. The presence of omega-3 fatty acids also inhibits the formation of the omega-6-derived compounds. In addition to their beneficial effects in fighting off infection, the omega-6-derived signal compounds are linked to atherosclerosis and related heart disease problems. This is why omega-3 fatty acids are touted as a dietary way to avoid heart disease.

What is the richest known source of omega-3 fatty acids? Ta-da: fish oil! Why do old fish smell fishy? In a big part because of the spontaneous oxidation of those omega-3 fatty acids.

Canola oil can contain 10% alpha-linolenic acid, an omega-3 fatty acid. When you heat it up, especially as during high-temperature frying, the fatty acids will spontaneously oxidize. Voila! The smell of dead fish.

Aside from the dead fish smell when you cook with it, canola oil would, I think, be good for you, being a good source of omega-3 fatty acids. So use it on salads or in other situations where you don't have to heat it. And keep opened bottles in the fridge to inhibit oxidation.

-Paul W.

P.S.: A guide to the systemic naming system, which is actually straightforward and unambiguous, once you understand the rules:

All of the fatty acids are carboxylic acids, meaning that they end in an acidic group consisting of a carbon atom double-bonded to an oxygen and also to a hydroxyl (-OH) group. This is shown in text as -COOH. All of these are systemically named as "somethingorother-oic acid". It will be "-anoic acid" if the rest of the compound is unsaturated (has no carbon-carbon double bonds), "-enoic acid" if there is one unsaturated bond, "-dienoic acid" if there are two unsaturated bonds, "-trienoic acid" if there are three unsaturated bonds. The prefix (from Greek) tells how many carbon atoms there are in all. If there are double bonds, they are indicated by one or more numbers designating the carbon atom number, considering the carbon in the -COOH group as 1, and counting back from there.

Thus: "Octadec-" means 18. "Octadecanoic acid" thus has a carboxyl group on one end, 18 carbons total, and no unsaturated bonding. The culprit for the fishy stink of fried canola oil is 9,12,15-Octadecatrienoic acid--translation: "carboxylic acid (-oic), three double bonds (trien-), 18 carbon atoms in all (octadeca), double bonds at the 9th, 12th, and 15th carbons, counting from the carboxyl -COOH group as #1. And if you count from the end (the -CH3 group), the first double bond occurs at carbon 16--three from the end. Hence this is an omega ("last" in scientific Greek) three fatty acid.

Clear as cooking oil, right?

-Paul W.

Thank you, Paul.

Wow, that should close the book on canola oil! I had wondered whether the omega-3 connection between fish and canola oils might account for their shared characteristic but figured it for chemical coincidence. Thanks for the lesson, Paul.

What is the richest known source of omega-3 fatty acids? Ta-da: fish oil! Why do old fish smell fishy? In a big part because of the spontaneous oxidation of those omega-3 fatty acids.

In your otherwise excellent monograph , Paul, I'll take faint issue with this one statement. To most people, a "fishy" odor is associated with trimethylamine, a truly nasty-smelling, volatile molecule that results from the rapid breakdown of choline in fish. Humans, like most animals, are quite sensitive to the smells of dead animals -- a useful adaptation -- and those are generally thiols and amines. That's why some of the biogenic amines get such colorful names as putresecine and cadaverine. Having had the misfortune of working with all of the above, I'll gladly bathe in skunk juice rather than get exposed to those biogenic amines. YMMV, of course.

Mark Lipton

Digging back in my memory, there was a particularly odoriferous solvent we would sometimes use in electrochemical experiments. Pyridine, maybe? Not exactly a tertiary amine, but if it's the smell I remember... whew!

Digging back in my memory, there was a particularly odoriferous solvent we would sometimes use in electrochemical experiments. Pyridine, maybe? Not exactly a tertiary amine, but if it's the smell I remember... whew!

Yup, that would be pyridine (benzene with one carbon replaced by nitrogen): smelly, but not OTT. More of a problem is the hazard it presents to the male reproductive organs -- yipes!!

Mark Lipton

Sigh. Scientists are hotties. I have absolutely no idea what any of you are talking about, but please keep going.

Sigh. Scientists are hotties. I have absolutely no idea what any of you are talking about, but please keep going.

Now, Celia, if you were a guy responding to a woman on the forum that way, Stuart and/or Cowboy would be running out here with the bucket. However, I think it safe to assume that won't happen here!

(PS... I agree. Science geeks rule!)

[Robin Garr]

Science geeks rule!)

So what are English majors then?

Oh, right, I remember. "Will you have fries with that?"

Writers are second on my list, Robin.

Sigh. Scientists are hotties. I have absolutely no idea what any of you are talking about, but please keep going.

Don't make me get the bucket! It's got pyridine in it!

Sigh. Scientists are hotties. I have absolutely no idea what any of you are talking about, but please keep going.

P.S.: A guide to the systemic naming system, which is actually straightforward and unambiguous, once you understand the rules:

All of the fatty acids are carboxylic acids, meaning that they end in an acidic group consisting of a carbon atom double-bonded to an oxygen and also to a hydroxyl (-OH) group. This is shown in text as -COOH. All of these are systemically named as "somethingorother-oic acid". It will be "-anoic acid" if the rest of the compound is unsaturated (has no carbon-carbon double bonds), "-enoic acid" if there is one unsaturated bond, "-dienoic acid" if there are two unsaturated bonds, "-trienoic acid" if there are three unsaturated bonds. The prefix (from Greek) tells how many carbon atoms there are in all. If there are double bonds, they are indicated by one or more numbers designating the carbon atom number, considering the carbon in the -COOH group as 1, and counting back from there.
-Paul W.

I'll have to remember this line down at the singles bar.....

I'll have to remember this line down at the singles bar.....

Does your wife know you are hanging out down there?

It's ok, Princess, I'm sure John was speaking hypothetically. And anyway, science groupies don't hang out in bars. We tend to lurk around the science departments at universities, or puzzle shops, or astronomy supply stores. Hypothetically speaking, of course.

And magic shops. Very geeky pursuit, magic.

Oh we looooove magic shops...

Oh, and model railway shops, for the inner anorak in all of us..



Sorry gents, we hijacked your thread..

Sorry gents, we hijacked your thread..

Nah, we're not really sorry.

I suggest that the moderator please re-title this thread to "Leave it to Beaver."

Bob, it is, or can be, kosher (anything that has no animal derivation, other than wine, is kosher and parve as long as it's handled in a kosher facility), but I don't know about the Passover part- it wasn't around when I was a kid and learning about this stuff.

Stuart, I think that canola is OK for religious Sephardic Jews during Passover…

Best wishes,
E.Y.

But I don't speak Ladino!

Well, I'm Ashkenazi on my mother's side, Mizrahi on my father's, so I just don't worry about this stuff.

I'm late to this discussion but I teach this stuff so let me have a go at it.

OLEIC -- named after olive oil. We call it 18:0, 18 carbons with zero double bonds.

I tell my students -- when you add a double bond, you have to add something to the name.

LINOLEIC -- named after linseed oil (flax seed). 18:1 cis delta-9. In other words an unsaturation 1/2 way down the molecule which makes the linear OLEIC molecule shaped like a big "V".

When you add another double bond, you add something else. An "N"

LINOLENIC -- also from linseed oil. This does have a smell but it's like a painter's studio, artists' oil paints are rich in linolenic acid.

I agree with Mark that most of the worst smells either have to do with nitrogen or sulfur compounds, and these fatty acids have none of the above. Of course Valeric acid is pretty distressing stuff and that also doesn't -- Valeric acid smells like the intense purified essence of sweat socks left in the gym for an entire semester and used regularly. Butyric acid is even worse, basically you smell it and you think (and maybe do) "VOMIT." But those are short chain acids, 4 or 5 carbons, and the acids above are 18 carbons long.

LINOLEIC and LINOLENIC are "essential" fatty acids. You need some in your diet to be able to continue to live. They are like vitamins. OTOH if you are on a lettuce only diet, you will still get plenty of these 2 oils.

My take on the Canola controversy -- I tried Canola years ago, and thought it smelled bad, and quit using it. Only a couple of years ago, my idol and demi-God, Thomas Keller, told me (in a couple of big fat cookbooks) to go buy some Canola Oil and use it. So I did. And I found that to my palate, in the uses prescribed by Keller, today's Canola is very mild and bland and completely inoffensive. Of course I don't do anything moronic like frying French Fries in it. I haven't reviewed whether the uses Keller prescribes are medium temperature uses but it occurs to me that that is quite possible.

Even when I didn't like the smell years ago I don't remember dead fish. More like waxy candles or plastic or something.

If this is a genetic difference in olfaction it is one of very many. Vive la difference.

Frank